The present invention relates to an illumination optical system used in an image display apparatus such as a projector which displays an image formed by controlling a direction in which outgoing light is polarized using a spatial light modulator such as a micro mirror array and in an image exposure apparatus which exposes a light-sensitive material to light bearing the thus formed image.
At present, a two-dimensional spatial light modulator such as a micro mirror array (hereinafter, referred to as “MMA”) which is commercially available as, for example, a Digital Micromirror Device™ (DMD) manufactured by Texas Instruments Inc. that create a two-dimensional image by controlling the deflecting angles of fine mirrors (micro mirrors) disposed two-dimensionally are widely utilized in image display apparatuses such as projectors for displaying an image, exposure/recording apparatuses for recording an image on a light-sensitive material by exposure to light bearing the image, and image exposure apparatuses such as a light molding apparatus using a photo-curing resin, and so on.
The MMA is a two-dimensional spatial light modulator having a plurality of rectangular micro mirrors which rotate about predetermined rotation axis, which are used to reflect incident light from an illumination light source to thereby form outgoing light, and optionally switch the deflecting direction of the outgoing light. The rotational angle of each micro mirror can be switched between +10° and −10° by rotating it making use of electrostatic force, and the deflecting direction of the outgoing light formed by reflecting the incident light can be switched for each micro mirror between the two rotational angles. Thus, the deflecting direction of each micro mirror can be controlled so that the outgoing light in the deflecting direction can bear an On- or Off-modulated image. Accordingly, the outgoing light in the deflecting direction can be referred to as activated light and deactivated light, respectively.
For example, in a projector 100 making use of an MMA shown in FIG. 8, light emitted from a light source lamp 102 passes through a lens group 104 and is reflected by a mirror 106, and then is incident on an MMA 108 as incident light. In contrast, since the deflecting angle is set for each micro mirror of the MMA 108, the incident light is reflected in a predetermined deflecting direction to form outgoing light, which travels toward a direction where a projection lens 110 is disposed, passes therethrough and is imaged on a screen 112, whereby an image is projected.
The light incident on the MMA 108 after having been reflected by the mirror 106 and the outgoing light after reflection by the micro mirrors of the MMA 108 has a relationship as shown in FIG. 9.
That is, the incident light Lin′ from the mirror 106 is incident on the MMA 108 such that the principal ray thereof forms an inclination angle of 20° with respect to a normal line to the surface on which the micro mirrors of the MMA 108 are arranged. In contrast, in a state in which the rotational angle of the micro mirror of the MMA 108 is set at +10°, a normal direction to the micro mirror surface is a direction C shown in FIG. 9, and outgoing light Lon′ (activated light) having a principal ray in a direction perpendicular to the surface on which the micro mirrors of the MMA 108 are arranged is caused to outgo. That is, the outgoing light Lon′ having the principal ray in a direction that agrees with the optical axis of the projection lens 110 is caused to outgo thereto. Since the principal ray of the outgoing light Lon′ is caused to agree with the optical axis of the projection lens 110 as described above, it is possible to make a lens performance to effectively act on the outgoing light Lon′ by minimizing a load on the projection lens 110.
In contrast, when the rotational angle of the micro mirror is set at −10°, a normal direction to the micro mirror surface is a direction D shown in FIG. 9, and outgoing light Loff′ (deactivated light) having a principal ray in a direction of 40° downward in FIG. 9 with respect to the normal line to the surface on which the micro mirrors of the MMA 108 are arranged is caused to outgo.
Incidentally, in the projector 100 described above, it is required to broaden the light flux divergent/convergent angle of the incident light Lin′ because it is desired to increase the quantity of the incident light Lin′ as much as possible in order to brightly project an image on the screen 112. However, the light flux divergent/convergent angle of the incident light Lin′ is restricted because it is necessary for the incident light Lin′ not to overlap the outgoing light Lon′ from which a problem is arisen in that the quantity of the incident light Lin′ cannot be increased.
In the example shown in FIG. 9, the light flux divergent/convergent angle of the incident light Lin′ is restricted to 20° or less from its relationship to the outgoing light Loff′, and the light flux divergent/convergent angle corresponds to F 2.8 in term of F number.
Ordinarily, in the apparatus as described above, an illumination optical system is designed with an F number of about 3.0 or more such that the incident light Lin′ cannot overlap the outgoing light Loff′. Accordingly, there is a problem in that the quantity of incident light on the two-dimensional spatial light modulator such as the MMA cannot be increased because of the restriction of the light flux divergent/convergent angle of the incident light to the level of F 3.0 more at which higher brightness cannot be provided.
These problems are not limited to the image display apparatus such as the projector, but are common to apparatuses including the illumination optical system using the spatial light modulator such as an exposure apparatus that records an image formed using the spatial light modulator on a light-sensitive material by exposure, and a light molding apparatus.